Preterm neonates in the Neonatal Intensive Care Unit (NICU) frequently suffer necessary but painful diagnostic and therapeutic procedures. The cumulative effects of repeated painful procedures on the developing brain may be of greater biological and clinical importance than previously recognized. Pain research in neonates has focused primarily on behavioral and physiologic responses by studying health, full-term infants, and older physiologically stable preterm infants. The relationship between sound and light levels in the NICU and preterm infants' arousal (sleep and wake patterns) with their responses to pain has not been investigated. The specific aims of this study are to examine the relationship between (a) sound (Lmax) and light (foot-candles) levels as environmental variables in the NICU, (b) arousal level of neonates (Als State Score for sleep and wake patterns), and (c) physiologic and behavioral responses (heart rate, oxygen saturation, Premature Infant Pain Profile (PIPP) score) of preterm infants prior to and following a painful stimulus - a heelstick for necessary blood sampling. Both immediate responses to the painful procedure and time to recover from the procedure (return to baseline, pre-procedure physiological and behavioral levels) will be studied. This research will also examine whether the relationships between sound, light, and arousal levels in the 2 hours preceding the heelstick procedure and preterm infants' responses to pain are moderated by gestational age. A convenience sample of 102 preterm infants (stratified into two equal gestational age groups: 25-27 weeks and 34-36 weeks) will be observed in the NICU. Physiologic responses to pain will be measured using the infant's bedside cardiorespiratory monitor and pulse oximeter. Sound and light levels will be collected using sound and light meters, respectively. Physiologic and environmental data will be collected, synchronized, and stored using a computerized data acquisition system. Data will be analyzed using general linear models (GLMs) and hierarchical regression analyses. The long-term aims of this research are to investigate nursing interventions that (a) minimize infant acute physiologic and behavioral responses to pain by promoting optimal NICU environment and arousal (sleep/wake) patterns for hospitalized neonates, (b) to improve pain assessment techniques in critically ill preterm neonates, and ultimately, (c) to decrease long-term neurobehavioral sequelae of chronic, repetitive pain experiences.